Wherever any great length of piping is used to carry fluids under pressure there is to be some leakage and this is particularly true of newly installed or assembled piping, such as water mains when first layed where considerable leakage is expected. Self-sealing procedures are routine, causing leakage at the joints to decrease rather quickly, but to insure reasonable integrity of the piping an inspection is ordinarily mandatory as, for example, before trenches for water mains are back-filled. The leakage is sometimes expressed in gallons per day per inch diameter and mile of pipe, but municipal inspectors may set limits on the order of two pints for a short test period in the case of approximately 1,000 feet of eight inch diameter pipe. The prescribed pressure for the test is about fifty percent in excess of the design or working pressure and the number of joints in the test section is a factor. The pipe section, in prior art systems, is isolated by closing any gates in the line and using headers or plugs so that all lateral and end openings are closed, and the pipe is filled with water and placed under pressure by a power driven water pump, or sometimes by air when no water is available. The water needed to maintain the pressure is measured, the pressure being monitored sometimes by an ordinary household meter. Measurement may also be made in terms of loss in pressure in a given time called the test period, usually that length of time required by local water department authorities, usually twenty minutes to one hour, or water is again pumped into the line to bring the pressure back to its initial value and the amount of water so pumped is measured. This measurement is often notoriously imprecise, especially perhaps when a tank is used as a source of the water. This inaccuracy arises in part from the difficulty in reading the water level in such a tank which is invariably heavy and awkward to level and necessarily large so that reading the water level may introduce appreciable error, being complicated by the meniscus effects and further complicated by the fact that the water level must be read twice, thus possibly doubling the error. In view of these facts there is a need for a simple, accurate method for such hydrostatic testing, a method which can be employed with a small portable apparatus with safety, reasonable expedition and certitude to assure convincing readings.